This document describes the specifications of the CZCS Level-1A archive products which are produced and distributed by the NASA Goddard Space Flight Center's Ocean Color Data Processing System (OCDPS). The products are implemented in the Hierarchical Data Format (HDF), and HDF terminology is used in this document.
These specifications are given in terms of the logical implementation of the products in HDF and are not a physical description of file contents. Therefore, HDF software must be used to create or read these products.
A CZCS Level-1A product is generated from CRTT data files. It contains some of the CRTT data (raw radiance counts from all bands as well as some data quality information), calibration and navigation data, and instrument and selected spacecraft telemetry that are reformatted. This product is stored as one physical HDF file.
Each product contains full resolution data with the type designated LAC for Local Area Coverage. The data in the file comprises a scene of approximately 2 minutes of satellite data. The scenes selected during the day only partially cover the earth.
The form of a Level-1A file name is Cyyyydddhhmmss.L1A_LAC, where C is for CZCS, yyyydddhhmmss are the concatenated digits for the GMT year, day of the year, hours, minutes, and seconds of the first scan line. Merged CZCS files are produced from all the individual L1 files in an orbit, to remove redundant scan lines. The form for these files is Cyyyydddhhmmss.L1A_MLAC. Examples of file names is:
For global attributes that have constant values specific to this product type, the value is given.
Product Name (character): the name of the product file (without path).
Title (character): "CZCS Level-1A Data".
Data Center (character): "NASA/GSFC SeaWiFS Data Processing Center" (*).
Station Name (character): "NASA/GSFC SeaWiFS Data Processing Center" (*).
Station Latitude (4-byte real): 38.9958 (*).
Station Longitude (4-byte real): -76.8511 (*).
Mission (character): "Nimbus CZCS".
Mission Characteristics (character): "Nominal orbit: inclination = 99.3 (Sun-synchronous); node = 1152 AM local (ascending); eccentricity = <0.0009; altitude = 855 km; ground speed = 6.4 km/sec".
Sensor (character): "Coastal Zone Color Scanner (CZCS)".
Sensor Characteristics (character): "Number of bands = 6; number of active bands = 6; wavelengths per band (nm) = 443, 520, 550, 670, 750, 11500; bits per pixel = 8; instantaneous field-of-view = 0.865 mrad; pixels per scan = 1968; scan rate = 8/sec".
Data Type (character): "LAC" or "MLAC".
Replacement Flag (character): "ORIGINAL" if this is the first version of this product delivered to the DAAC; otherwise, it is set to the name of the product to be replaced (superseded) by the present product.
Software ID (character): identifies version of the operational software used to create this product (**).
Processing Time (character): local time of generation of this product; concatenated digits for year, day-of-year, hours, minutes, seconds, and fraction of seconds in the format of YYYYDDDHHMMSSFFF.
Input Files (character): the name of the CRTT file (without path) from which the current product was created. This information is stored in the product as part of its processing history.
Processing Control (character): all input and processing control parameters used by the calling program to generate the product. Vertical bars or carriage return characters serve as parameter information delimiters. This information is stored in the product as part of its processing history.
Start Time (character): start GMT of the first scan line of the scene; concatenated digits for year, day-of-year, hours, minutes, seconds, and fraction of seconds in the format of YYYYDDDHHMMSSFFF.
End Time (character): start GMT of the last scan line of the scene; concatenated digits for year, day-of-year, hours, minutes, seconds, and fraction of seconds in the format of YYYYDDDHHMMSSFFF.
Scene Center Time (character): start GMT of the center scan line of the scene; concatenated digits for year, day-of-year, hours, minutes, seconds, and fraction of seconds in the format of YYYYDDDHHMMSSFFF.
Start Year (2-byte integer): GMT year of first scan line of the scene.
Start Day (2-byte integer): GMT day-of-year of first scan line of the scene.
Start Millisec (4-byte integer): GMT milliseconds-of-day of the first scan line of the scene.
End Year (2-byte integer): GMT year of last scan line of the scene.
End Day (2-byte integer): GMT day-of-year of last scan line of the scene.
End Millisec (4-byte integer): GMT milliseconds-of-day of the last scan line of the scene.
Start Node (character): "Ascending"; describes node direction at the start of the scene.
End Node (character): "Ascending"; describes node direction at the end of the scene.
Orbit Number (4-byte integer): orbit number of the scene.
Pixels per Scan Line (4-byte integer): 1968.
Number of Scan Lines (4-byte integer): number of scan lines in the scene.
Number of Pixel Control Points (4-byte integer): number of pixels in the latitude and longitude control point arrays.
Number of Scan Control Points (4-byte integer): number of lines in the latitude and longitude control point arrays.
LAC Pixel Start Number (4-byte integer): the LAC pixel number corresponding to the first pixel in scan lines of this product if subsetted; value of 1.
LAC Pixel Subsampling (4-byte integer): the subsampling rate for the pixels in this product relative to LAC scan lines if subsetted; value of 1.
Scene Center Scan Line (4-byte integer): number of the center scan line (1-relative) of the scene, relative to first scan line.
Filled Scan Lines (4-byte integer): not used.
Sensor Tilt (4-byte real): CZCS sensor tilt while the dataset was being acquired. If MLAC, this is the tilt for the first file of the orbit.
Gain (4-byte integer): CZCS gain setting used. If MLAC, this is the gain for the first file of the orbit.
Thresh (4-byte integer): An integer value of 1 (off) or 2 (on) indication the status of the CZCS threshold function for the scene.
Calibration Slope (4-byte real, array size 6): Slope to use for the conversion of the 8-bit counts into radiometric units (mw/cm^2 sr um). If MLAC, this is the slope of the initial file in the orbit.
Calibration Intercept (4-byte real, array size 6): Intercept to use for the conversion of the 8-bit counts into radiometric units (mw/cm^2 sr um). If MLAC, this is the intercept of the initial file in the orbit.
Center Roll (4-byte real): Spacecraft roll at the geographic center of the scene. If MLAC, the roll for the first scene in the orbit.
Center Pitch (4-byte real): Spacecraft pitch at the geographic center of the scene. If MLAC, the pitch for the first scene in the orbit.
Center Yaw (4-byte real): Spacecraft yaw at the geographic center of the scene. If MLAC, the yaw for the first scene in the orbit.
ILT Flags (unsigned byte): summary of information available in the CZCS-ILT for the data. From the most significant bit, they are: 1 - summary: all relevant data available, 2 - time corrections available, 3 - solar ephemeris available, 4 - data quality loss available, 5 - VIP data available, 6 - spacecraft ephemeris (2 bits): 00 - not available, 01 - predictive, 11 - definitive. Except for spacecraft ephemeris, a 1 indicates availabiltity.
Parameter Presence Code (unsigned byte): The top 6 bits of this indicate the presence (with a 1) of data for the CZCS bands 1 - 6.
Number of Missing Scan Lines (2-byte integer): number of missing scans in this dataset.
Number of Scans with Missing Channels (2-byte integer, array size 6): for each band, the number of scans without channel data.
Number of HDT Sync Losses (2-byte integer): number of sync losses while reading the HDT(p) tape.
Number of HDT Parity Errors (2-byte integer): number of parity errors while reading the HDT(p) tape.
Number of WBVT Sync Losses (2-byte integer): number of sync losses detected by pre-processor during generation of HDT(p) tape.
Number of WBVT Slip Occurrences (2-byte integer): number of bit slip occurrences detected by pre-processor during generation of HDT(p) tape.
Note that the Upper / Lower, Right / Left, and Start / End Center Latitude and Longitude values in this section are relative to the arrays stored in the file. As CZCS takes data while the satellite is ascending, this means that Upper, Lower... do not correspond to North and South.
Latitude Units (character): "degrees North"; units used for all latitude values in this product.
Longitude Units (character): "degrees East"; units used for all longitude values in this product.
Scene Center Latitude (4-byte real): latitude of the nadir point of the scene's center scan line.
Scene Center Longitude (4-byte real): longitude of the nadir point of the scene's center scan line.
Scene Center Solar Zenith (4-byte real): solar zenith angle of the nadir point of the scene's center scan line.
Upper Left Latitude (4-byte real): latitude of the upper left scene corner.
Upper Left Longitude (4-byte real): longitude of the upper left scene corner.
Upper Right Latitude (4-byte real): latitude of the upper right scene corner.
Upper Right Longitude (4-byte real): longitude of the upper right scene corner.
Lower Left Latitude (4-byte real): latitude of the lower left scene corner.
Lower Left Longitude (4-byte real): longitude of the lower left scene corner.
Lower Right Latitude (4-byte real): latitude of the lower right scene corner.
Lower Right Longitude (4-byte real): longitude of the lower right scene corner.
Northernmost Latitude (4-byte real): northernmost latitude of all scan line end points.
Southernmost Latitude (4-byte real): southernmost latitude of all scan line end points.
Westernmost Longitude (4-byte real): westernmost longitude of all scan line end points.
Easternmost Longitude (4-byte real): easternmost longitude of all scan line end points.
Start Center Latitude (4-byte real): latitude of center pixel for first scan line.
Start Center Longitude (4-byte real): longitude of center pixel for first scan line.
End Center Latitude (4-byte real): latitude of center pixel for last scan line.
End Center Longitude (4-byte real): longitude of center pixel for last scan line.
The three groups of data objects -- Scan-Line Attributes, Raw CZCS Data, and Navigation -- contain data that are functions of scan lines. That is, each data object within these groups has data for each scan line and is therefore dimensioned by the value of the global attribute, Number of Scan Lines.
The following data objects are SDSs belonging to the Vgroup "Scan-Line Attributes". Attributes of the SDSs are shown in bold.
msec (4-byte integer, array size Number of Scan Lines): long_name = "Scan-line time, milliseconds of day"; valid_range = (0,86399999); units = "milliseconds".
slat (4-byte real, array size Number of Scan Lines): long_name = "Scan start-pixel latitude"; valid_range = (-90.,90.).
slon (4-byte real, array size Number of Scan Lines): long_name = "Scan start-pixel longitude"; valid_range = (-180.,180.).
clat (4-byte real, array size Number of Scan Lines): long_name = "Scan center-pixel latitude"; valid_range = (-90.,90.).
clon (4-byte real, array size Number of Scan Lines): long_name = "Scan center-pixel longitude"; valid_range = (-180.,180.).
elat (4-byte real, array size Number of Scan Lines): long_name = "Scan end-pixel latitude"; valid_range = (-90.,90.).
elon (4-byte real, array size Number of Scan Lines): long_name = "Scan end-pixel longitude"; valid_range = (-180.,180.).
tilt (4-byte real, array size Number of Scan Lines): long_name = "Tilt angle for scan line"; valid_range = (-20.1,20.1); positive values indicate aft tilts and negative values indicate forward tilts; units = "degrees".
The following data objects are SDSs belonging to the Vgroup "Raw CZCS Data". Attributes of the SDSs are shown in bold.
band1 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band1 data"; units = "radiance counts". Data is stored pixels running fastest.
band2 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band2 data"; units = "radiance counts". Data is stored pixels running fastest.
band3 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band3 data"; units = "radiance counts". Data is stored pixels running fastest.
band4 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band4 data"; units = "radiance counts". Data is stored pixels running fastest.
band5 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band5 data"; units = "radiance counts". Data is stored pixels running fastest.
band6 (unsigned byte, array size Number of Scan Lines x Pixels per Scan Line): long name = "Level-1A band6 data"; units = "radiance counts". Data is stored pixels running fastest.
cal_sum (unsigned byte, array size Number of Scan Lines x 5): long_name = "Calibration quality summary"; 5 values indicating the quality of each line of data, a 0 if good and a 1 if the data has this condition: (1) questionable ephemeris, (2) questionable spacecraft attitude, (3) at least one of the expected channels was not present, (4) at least one of the expected channels had active calibration value outside expected range, (5) at least one of the expected channels had voltage staircase count outside expected range.
cal_scan (unsigned byte, array size Number of Scan Lines x 6): long_name = "Calibration quality per Scan"; for each band, a value indicating non-0 if data for the channel is expected but not present.
The following data objects are SDSes belonging to the Vgroup "Navigation". Attributes of the SDSs are shown in bold. The control point arrays latitude and longitude contain the navigation information for processing and display.
orb_vec (4-byte real, array size Number of Scan Lines x 3): long name = "Orbit position vector at scan line time"; valid_range = (-7200.,7200.); units = "kilometers"; used to determione spacecraft position for geolocation. Note that this extry is not defined if the pos_err SDS has a value < 0 for that line.
att_ang (4-byte real, array size Number of Scan Lines x 3): long name = "Computed yaw, roll, pitch at scan line time"; valid_range = ( -180., 180. ); units = "degrees"; Attitude of the spacecraft at the time of the scan line.
pos_err (4-byte real, array size Number of Scan Lines): long name = "Orbit position error"; valid_range = ( -10., 7200.); units = "meters"; Orbit position error in interpolated segments. This is < 0 if no orbit information is available for the CZCS granule (in orb_vec), 0 if the data is not interpolated and >= 0 to indicate the expected maximum error in the orbit. In cases where no orbit data exists or the position error is over a threshold, the satellite geometry is computed from general orbit data and pixel latitude and longitude.
cntl_pt_cols (4-byte integer, array size Number of Pixel Control Points): long_name = "Pixel control points"; units = "none"; array of pixel indices corresponding to latitude and longitude SDSs.
cntl_pt_rows (4-byte integer, array size Number of Scan Control Points): long_name = "Scan control points"; units = "none"; array of scan line indices corresponding to latitude and longitude SDSs.
longitude (4-byte real, array size Number of Scan Control Points x Number of Pixel Control Points): long_name = "Longitudes at control points"; valid_range = "(-180., 180.)"; units = "degrees"; longitudes of pixels indicated by cntl_pt_cols and cntl_pt_rows.
latitude (4-byte real, array size Number of Scan Control Points x Number of Pixel Control Points): long_name = "Latitudes at control points"; valid_range = "(- 90., 90.)"; units = "degrees"; latitudes of pixels indicated by cntl_pt_cols and cntl_pt_rows.
gain (2-byte integer, array size Number of Scan Lines): long name = "Gain setting at scan line time"; valid_range = ( 1, 4 ); units = "none"; Gain setting at the scan line time.
slope (4-byte real, array size Number of Scan Lines x 6): long name = "Calibration slope at scan line time"; valid_range = ( -20., 20. ); units = "mW cm^-2 um^-1 sr^-1 count^-1".
intercept (4-byte real, array size Number of Scan Lines x 6): long name = "Calibration intercept at scan line time"; valid_range = ( -20., 20. ); units = "mW cm^-2 um^-1 sr^-1".
